A decent A3 scanner will cost more than the PC. Try this one: click here
Nothing much wrong with the CTX monitor, but most people say that TFT monitors are much easier on the eyes. A 17" TFT monitor will be not much more than a 19" CRT but has a similar work area.
I am not sure about graphics cards, but I don't think you need top of the range, as long as you have a DVI output.
Look here for some ideas for your website. Rather a nicely designed site, though some of the earleir scans that she did are too dark:
A Virtual Art Museum: click here
To create the website, look at Netobjects Fusion: click here
To resize the scans to make thumbnails and to convert from TIFF to JPG or PNG try Irfan View. Much handier than Photoshop for simple tasks: click here